A key component of a helicopter is the main rotor hub. It provides attachment of the main rotor blades during operation. Rotational power is delivered to the main rotor hub to provide rotational velocity to the blades in order to create aerodynamic lift. The main rotor hub must allow for rotational motion of the blades in the vertical (flap), horizontal (lead-lag), and axial (pitch) directions near the blade root attachment with the hub to accommodate flight control authority and dynamic stability. Main rotor hub systems that accommodate these motions with discrete hinge mechanisms are referred to as fully articulated hubs. Through out the history of the helicopter, engineers have struggled to provide these rotational freedoms with bearing systems that can accommodate high frequency and high amplitude oscillatory motion under high trust loading created by the centrifugal force of the rotating blades. Elastomeric bearings have become an industry standard for accommodating flap-wise motion in articulated hub systems. These bearings are composed of elastomeric material that allows for shear compliance within the elastomer, and for rotational freedom while reacting radial centrifugal force in compression.
Elastomeric conical bearings are commonly used in bearing assemblies for helicopter rotor systems to accommodate rotor motion. The bearing assemblies are axially preloaded to prevent the conical bearing elements from experiencing a resultant tensional load. Currently, mono-directional bearing elements are employed at each attachment site of the main rotor hub. FIG. 1 depicts a view of a prior art articulated hub assembly 20a. The hub assembly 20aincludes a tie bar 26 connected to a hub center body 22. Each bearing assembly 30a includes a conical bearing elements 52 contacting the journal 28 on the bearing's inner surface 52 and the outer bearing surface is contained within an outer housing 42a. Each bearing assembly also includes a mono-directional single conical taper elastomeric bearing element 54 contained within. The conical bearing elements 52 are arranged such that the apex of the conical bearing elements 52 extends radially outward from one another. The bearing arrangement yields a force couple that extends from one bearing to the other. The force couple yields a bearing pre-load path 43 extending through the hub center body 22.
The prior art design creates an extended force couple resulting in a bearing pre-load path extending through the main rotor hub center body. The hub center body must be designed to carry the extra loading. The extra design requirements add weight to the overall rotor hub reducing the aircraft's load capacity and fuel efficiency.